This invention relates to a method and apparatus for controlling the amount of fuel metered, through electrically-controllable valve means, to an internal combustion engine.
As used herein, the term "binary number" means a number represented by a plurality of bits of information having either of two states.
A "Method and Apparatus for Engine Control" is described in U.S. patent application Ser. No. 423,968 filed Dec. 12, 1973 in the names of D. F. Moyer, S. S. Devlin and R. J. Genik, now U.S. Pat. No. 3,696,614. The engine control system described in this patent employs a digital computer to calculate arithmetically and repetitively values corresponding to settings of means for controlling the engine spark timing, the exhaust gas recirculation (EGR) valve and the amount of fuel metered to the engine. The digital computer calculates the values for these controlled variables arithmetically from algebraic functions describing desired relationships between the controlled variables and various engine operating conditions. Preferably, the relationships between the controlled variables and changing engine conditions take into account the interaction of the controlled variables, thereby, to achieve those conditions of control that result in stable engine operation. The settings of the controlled variables are updated repetitively, for example, every 30 milliseconds (ms) or every quarter-revolution of the engine crankshaft.
A digital microprocessor and memory system, using MOS technology with a 12-bit data and address format, was used in reducing the present invention to practice. This system is currently commercially available in Japan from the Tokyo Shibaura Electric Company of Japan. This company, however, is undertaking a new MOS 12-bit microprocessor design that is expected to be commercially available in the United States in the latter part of 1976. The new design is the microprocessor preferred for use in the practice of the present invention. Of course, other known microprocessors or minicomputers using different bit numbers could be used in a system operating according to the principles hereinafter described, among which are: the System-User-Engineering minicomputer of the Lockheed Electronics Company described in its publication entitled, "SUE Computer Handbook"; the Intel Corporation 8080; the Motorola 6800; the Fairchild F8; and the Rockwell PPS-8. Also, microprocessors are currently available from Texas Instruments, Inc., National Semiconductor Corp., Advanced Micro Devices and Siemens in both 8-bit and 16-bit versions.
In the microprocessor and associated logic circuits used in an engine control system of the type described in the Moyer et al patent, a substantial amount of computer time may be required to carry out the programmed computer calculations, and the time between updates of the calculated computer output values may be on the order of 30 ms. In an eight-cylinder, four-cycle internal combustion engine operating at 3,000 rpm, a combustion process takes place in one of the eight cylinders every five ms. Thus, between computer updates, there may be as many as six spark firings intended to produce combustion in an engine cylinder. During transient engine operating conditions, the air-fuel ratio of the mixture supplied to the engine cylinders may be such that misfires occur or poor or improperly timed combustion takes place.
The amount of fuel supplied to an engine at any instant, according to most engine control philosophies now in use, should be in the amount necessary to provide a substantially stoichiometric air-fuel ratio in the mixture supplied to each cylinder. In an engine control system employing a digital computer, any of several available designs of electrically-controllable valve means may be used to control the supply of fuel to the engine. For example, an electronically-controlled carburetor may be used or electromagnetic fuel injectors may be provided, one for each cylinder, and the fuel may be injected into the intake manifold just upstream of the intake valve for each of the engine cylinders. Alternatively, electromagnetic fuel injectors may be positioned within a central throttle body and fuel injected into the intake manifold or throttle body at a location upstream of all of the passages leading to the intake valves for the various engine cylinders.
Fuel injection systems that utilize electromagnetic fuel injectors control the fuel delivery to the engine by varying the width of the electrical pulse applied to each of the fuel injectors. The longer the pulse width, the greater is the amount of fuel delivered through the injector into the engine. The systems or controllers used to determine the fuel injector pulse width fall into either of two categories, the speed-density controller or the mass air-flow controller. The speed-density controller uses the absolute pressure within the intake manifold of the internal combustion engine in conjunction with the engine speed and other engine operating condition variables, such as engine temperature, atmospheric pressure, atmospheric temperature, etc., to determine indirectly the mass air flow into the engine. The mass air-flow controller directly measures the air flow into the intake manifold of the internal combustion engine and adjusts the fuel injector pulse width accordingly.
Internal combustion engines of recent design incorporate exhaust gas recirculation (EGR) to reduce the level of nitrogen oxide exhaust emissions. Typical prior-art fuel-metering systems of the speed-density type calibrate the fuel delivery system for some assumed and fixed EGR rate. However, it is desirable that the EGR flow rate be taken into account in determining the amount of fuel to be supplied to the engine, particularly during transient conditions.